WGT - Phones
Your phone should work in Germany if you come from Europe, if you are from further afield then you will need to check with your provider. The Phone network in Germany seems to be behind that of the UK, whilst we take 5G for granted it was not to be found in Leipzig last year. The key thing to remember is to disable mobile date before you land in Germany, else when you turn it on it will start updating apps and costing you money.
If you want to use your phones mobile data then its worth getting a roaming package (if your phone package is not free when in Germany), when you first turn on your phone in Germany your provide will normally send you a text message that will allow you to gain access for a nominal daily charge (although you may have to watch when the daily charge ends, I have found that it ends at midnight in a lot of cases, which either means you need to update your package in the middle of the night (although you should still be out partying), else your phone may revert to normal mobile data and start racking up your costs).
Most Hotels offer WiFi, some charge, some are free (although the bandwidth or free time may be limited). There are numerous hotspots around Leipzig where you can get free WiFi as many shops / cafes have it (the password can be found with the menu, or simply ask the staff).
A cheaper option maybe to install a limited sim card into your phone that uses one of the German networks, these can come as physical sim cards or e-sims if you have a newer phone. The vast majority of Germans use one of the three main carriers O2, T-Mobile, and E Plus.